The invention relates to digital subscriber line (DSL) transceivers. More particularly, the invention relates to power cutback configuration of DSL transceivers using public switched telephone network (PSTN) signaling.
DSL provides a subscriber with the ability to use a twisted-pair telephone line for both voice and data simultaneously. The frequency ranges supported by the twisted-pair line are divided into three or more bands and used for specific purposes. For example, 0-4 kHz can be used for voice communication, 30-138 kHz can be used for upstream data communications and 138+kHz can be used for downstream data communications. Upstream communications refers to data flow from the DSL modem to a service provider, while downstream communications refers to data flow from the service provider to the DSL modem. Other DSL standards also exist that use different frequency allocations.
The power levels at which DSL modems transmit upstream data must be carefully controlled so that the modem signals do not interfere with the voice communications over the twisted-pair line. Current power level configurations include providing a predetermined power cutback (e.g., 80%) for all applications of a particular modem model. These cutback levels are typically selected based on a worst case scenario basis. Providing a predetermined power cutback level for all DSL modems results in most modems operating at less than peak efficiency.
Power cutback is typically provided by one or more filters and/or gain control units. For example, the modem can include a bandpass filter that passes frequencies used for upstream communications and limit the upstream power to a fixed predetermined power level. However, such filters reduce flexibility because filters provided by a manufacturer are typically designed based on worst case scenarios. Flexibility may be provided by allowing a modem user or technician to change the filter power output, but this would require the user or technician to access the internal components of the modem, which may result in reduced efficiency or lifespan of the modem.